68 CLASS V. INSECTS. 



so. Those which are not winged continue, during their 

 whole existence, of the same form and structure as at birth. 

 Those which are winged undergo certain metamorphoses, or 

 changes of form, which will be hereafter described. They 

 all have six legs, with the exception of the millepedes, which 

 have always more ; and the number increases also witji their age. 



The bodies of insects are divided into head, trunk,' and 

 abdomen. The head is attached to the trunk by a joint or 

 articulation, which is movable in every direction. It is 

 destitute of a brain, but is furnished with a mouth, eyes, 

 and two antennae or feelers. These are a kind of filaments, 

 composed of joints, varying much in form and length, prob- 

 ably designed as the organs of the sense of touch, or of 

 sensations still more delicate, and of a nature totally unknown 

 to us. 



The mouth -of insects varies much in its construction, 

 according to the nature of their food. Some of them subsist 

 only upon the juices of animal and vegetable substances, and 

 have their lips arranged in the form of a tube or sucker ; 

 some of them are armed with a sort of lancet, with which 

 they are enabled to pierce the skin of animals ; some with a 

 kind of beak ; and others with a trunk or proboscis, which in 

 the butterflies is capable of being rolled up in a spiral form. 

 The insects which subsist upon solid substances are provided 

 with jaws, which generally act laterally instead of verti- 

 cally, and serve to masticate their food. Beside these parts, 

 many species are furnished with palpi, organs somewhat 

 resembling the antennae in structure and appearance, but 

 whose office is to bring the food to the mouth, and hold it, 

 while the insect eats. 



To the trunk are joined the legs, and the wings'when pres- 

 ent. It is divided, in those that have only six legs, into three 

 segments or divisions, to each of which one pair of legs is 

 attached. The legs are composed of four parts, called the 

 haunch, thigh, leg or shank, and foot ; which resemble con- 

 siderably the corresponding parts in the limbs of quadrupeds. 

 They vary in different insects, according to their habits and 

 modes of life. Thus, in the grasshopper, the hind pair are 

 very long and strong ; in the aquatic insects, they are flattened, 

 in order to answer the purpose of oars. The wings differ 

 much in kind and arrangement, as well as in number. Most 

 of the winged insects have four, but some only two. They 

 are generally thin, dry, membranaceous, and semi-transparent. 

 In the butterfly the membrane forming the wing is concealed 



